The present invention relates to a method and a device for adjusting, one or more projectors.
The initial aim of the invention is for it to be used to adjust one or more CRT (Cathode Ray Tube) projectors. However, in general terms it can also be used for other projectors, more particularly LCD (Liquid Crystal Display) projectors or so-called light valve projectors, as well as matrix-addressed projectors.
As is known, a CRT projector customarily comprises three cathode ray tubes, respectively a green, a red and a blue tube which are each able to generate a light beam, respectively in the colors mentioned above. The light from each of these cathode ray tubes is directed towards a common screen by means of projection means which are provided for this purpose, so that three separate pictures are formed, which are superposed on one another on the screen. By superposing the three colors and varying the intensity of these colors, it is possible to obtain different colors.
Owing to the fact that separate light beams are used, and moreover these light beams are produced separately and guided to the screen along different paths, various aberrations may occur, both between the different colors and relating to the light of one color.
Therefore, it is also clear that in order to obtain an optimum picture various corrections have to be carried out in order to minimize the aberrations mentioned above. As is known, it is possible to make provision for various corrections, including: convergence, geometry, focus, astigmatism, contrast modulation and gamma correction, as well as others, as will emerge from the description below.
It is also possible to provide corrections which aim to achieve a particular effect, for example in order to create so-called soft edge, the meaning of which is that the projected picture is gradually attenuated at the location of the edge, for example in order to prevent the formation of a brightly illuminated strip in the event of two projected pictures emanating from two projectors overlapping.
Furthermore, it is possible to provide corrections relating to the so-called adjoining geometry and/or overlapping geometry. The adjoining geometry is the geometry of pictures which are projected next to one another by two or more projectors. The overlapping geometry relates to pictures which are projected on top of one another by two or more projectors. This may arise both in the case of different pictures which are to form a single entity and in the case of identical pictures which are projected on top of one another in order to increase the light intensity.
A device and method for carrying out corrections of this nature have already been described in Belgian Patent Application No. 09600536 in the name of the current applicant. According to this application, the abovementioned corrections are brought about by splitting up a test picture which is projected onto the screen into one or more zones which are to be adjusted, by viewing the picture with the aid of a camera, the camera signal being digitized, by compiling a mathematical model with the aid of the digitized values obtained, and by using this mathematical model to form control signals in order to carry out the correction in question. In this case, the correction is carried out prior to normal use of the projector.
U.S. Pat. No. 5,136,390 has disclosed a method for correction which is intended to create a so-called soft edge, also known as xe2x80x9cseamless video displayxe2x80x9d, in such a manner that various pictures can be projected so as to overlap at their edges, in such a way that the light intensity at the location of the transition is such that this transition shows up to the least possible extent. According to this American patent, to do this, factors which are respectively associated with the intensity of the various parts or xe2x80x9cpixelsxe2x80x9d of the picture are stored in a memory. The intensity of the light is modified as a function of the location where it is incident on the screen, in accordance with the factor which has been stored for that pixel of the picture. By changing the factors mentioned above, it is thus possible to obtain various effects. According to U.S. Pat. No. 5,136,390, to do this the appearance of the projected picture is viewed and the desired changes are input via a keyboard of a computer. The drawback of this is that it is a very time-consuming operation and that correction of this nature is relatively inaccurate.
It should also be pointed out that the correction of soft edge is very subjective, since everyone""s perception of color is different. Since, according to U.S. Pat. No. 5,136,390 the feedback is manual and the mathematical model is therefore adapted manually, the result obtained depends on the person carrying out these amendments and on his/her perception of the projected picture. It is clear that this will not provide an optimum result for all viewers.
Moreover, it is clear that this method is only suitable for realizing such soft edge.
In U.S. Pat. No. 5,532,765 is described an apparatus for correcting images. Preferably tetrahedron shaped waveforms with rising and falling linear portions are generated. Therefrom a position of the centroid and a level of the image signal are calculated, on the basis of which error values are calculated. The position of the centroid and the error values are supplied to a correction signal generating circuit, which generates correction signals. These correction signals are supplied to a corrector in the display device.
The correction signal generating circuit includes a correction waveform generating circuit, which generates kinds of fundamental correction waveforms minimally required for correction. Correction data for each adjustment point is stored in a memory, and data interpolation is performed in the horizontal and vertical directions, thus creating a desired correction waveform. Nothing has been done to overcome known drawbacks of known interpolation methods.
A drawback of the apparatus described hereinabove is the fact that a specified test pattern is needed, which makes real-time error corrections impossible.
The object of the invention is to provide a method and device for adjusting one or more projectors, making it possible to optimize the method and device described in BE 09600536 while avoiding various drawbacks of the system described in U.S. Pat. No. 5,136,390 in the event that the correction is used for the so-called soft edge application.
To this end, the invention provides a method for adjusting one or more projectors, each projector generating a number of light beams of different color, characterized in that the projected picture is automatically adjusted during normal use of the projector. Owing to the fact that the projected picture is adjusted during normal use of the projector, i.e. during projection to the public, it is always possible to obtain an optimum picture, or at least to attempt to obtain an optimum picture. It is thus possible to prevent errors which arise from the fact that certain corrections are affected by factors which are not known or do not have any influence during the initial correction.
In a preferred embodiment, the projected picture will be at least adjusted via a feedback.
In a particular embodiment, mathematical models which are based on the influencing factors which are relevant for the particular adjustment will be used for carrying out the adjustment.
According to another particular aspect of the invention, the mathematical models, during use of the projector, are adapted as a function of the result obtained.
According to the invention, the adjustment can be carried out while the projector is in use, on the basis of the various signals. To this end, it is possible, for example, to make use of a signal emanating from a cameras which is directed at the picture.
According to a variant, it is also possible to make use of a video signal which does not necessarily emanate from the abovementioned camera. More particularly, in this case, use will be made of the video signal which is supplied to the input, in other words the signal which comprises the picture which is to be projected.
The invention also provides for a special interpolation technique which can be used in the method mentioned above. According to the invention, this interpolation technique may also be used in projectors which do not employ the abovementioned method of automatic adjustment during normal use of the projector.
According to the invention, to carry out the interpolation, a number of basic waveforms are used, for at least three successive adjustment-point locations, data relating to the directional coefficients of the connecting lines between the values associated with these adjustment-point locations is collected, and a choice is made about the basic waveforms used to carry out the interpolation as a function of this data relating to the directional coefficients.
This interpolation technique is particularly suitable for using a limited number of observed points to determine intervening points, in which case this may involve data observed by a camera and data stored in a memory.
Furthermore, the invention also relates to a device, more particularly an electronic circuit, for carrying out the method mentioned above, and to projectors which are equipped with a device of this nature.
The characteristic features of the abovementioned interpolation technique and device will emerge from the following description.